In the formation of integrated circuits, the components of the integrated circuits need to be patterned to form desirable shapes. A typical patterning process includes a lithography process, which includes coating a photo resist over a target layer that is to be patterned, exposing the photo resist using a lithography mask, developing the photo resist, and using the developed photo resist to etch the target layer. As a result, the layout of the developed photo resist is transferred to the underlying layer. The photo resist is then removed.
The lithography process may be performed using an inline process or an offline process. In the inline process, all steps of the pattern formation of the photo resist are performed in a same production tool, which pattern formation includes photo resist coating, soft baking, exposing the photo resist, post-exposure baking, and developing the photo resist. In the offline process, the above-recited process steps are separated into different production tools including, for example, a production tool for the photo resist coating and a production tool for the exposure and the development of the photo resist. The wafers with the photo resist coated thereon are transferred between the production tools.
During the transferring, the wafers and the respective photo resist are subject to the effect of various detrimental chemicals, which include airborne amine. The amine will neutralize the photo acid that is generated in the photo resist after exposure. Hence, the amount of photo acid is undesirable reduced. This causes the variation in the dimensions of the features generated by the lithography process. For example, due to the undesirable exposure to amine, the trenches formed using the lithography process is reduced, and the line Critical Dimension (CD) is undesirably increased.